A resonant cavity is a hollow volume that stores standing waves. In an electrical context, at least one conductive wall defines an outer surface of the resonant cavity. A probe in the middle of the volume may guide the waves in a desired manner. This probe, also known, as a “puck,” may be metallic, ceramic, or made of other materials. The paragraphs below describe a resonant cavity that may include a ceramic puck, often called a “dielectric resonator.”
A dielectric resonator is an electronic component that exhibits resonance for a narrow range of frequencies, generally in the microwave band. Resonators are used in, for example, radio frequency communication equipment. In order to achieve the desired operation, many resonators include a “puck” disposed in a central location within a cavity that has a large dielectric constant and a low dissipation factor.
The combination of the puck and the cavity imposes boundary conditions upon electromagnetic radiation within the cavity. The cavity has at least one conductive wall, which may be fabricated from a metallic material. A longitudinal axis of the puck may be disposed substantially perpendicular to an electromagnetic field within the cavity, thereby controlling resonation of the electromagnetic field.
When the puck is made of a dielectric material, such as ceramic, the cavity may resonate in the transverse electric (TE) mode. Thus, there may be no electric field in the direction of propagation of the electromagnetic field. While many TE modes may be used, dielectric resonators may use the TE011 mode for applications involving microwave frequencies. Using the TE011 mode as an exemplary case, the electric field will reach a maximum within the puck, have an azimuthal component along a central axis of the puck, generally decrease in the cavity away from the puck, and vanish entirely along any conductive cavity wall. The magnetic field will also reach a maximum within the puck, but will lack an azimuthal component.
When combining more than one dielectric resonator, a designer will need to couple electromagnetic energy from the first cavity to the second cavity. Such coupling may be difficult if the first cavity is distant from the second cavity. Coupling may also require the careful fabrication of apertures connecting the first and second cavities. These apertures may be tuned in a factory to compensate for manufacturing tolerances.
Despite such tuning, it may be difficult to build a filter that couples multiple cavities or dielectric resonators together to define a desired frequency range. Conventional attempts to provide specified spectra had been both impractical and expensive. These tuners have used many parts and tedious techniques that make it difficult to adjust coupling between resonant cavities or dielectric resonators.
Accordingly, there is a need for an improved coupler that provides tuning over a wide range of frequencies. More particularly, there is a need for a coupler that can be used in wide bandwidth filters. There is also a need for a cost effective technique that couples high dielectric resonators.